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Comment:In ORDER BY LIMIT queries, try to evaluate the ORDER BY terms first, and it it becomes clear that the row will not come in under the LIMIT, then skip evaluation of the other columns.
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SHA3-256:c381f0ea57002a264fd958b28e4921cb9c9e73a10fb592f6bb64e6bc9bd16d39
User & Date: drh 2018-05-03 23:20:06
References
2018-05-05
16:50
In an ORDER BY LIMIT, make sure the ORDER BY expression evaluator does not try to reuse values from the result set if the result set has not yet be computed. This fixes a bug in the recent deferred-row loading optimization, check-in [c381f0ea57002a264fd958b28e]. OSSFuzz discovered the problem. check-in: 5d61e75f user: drh tags: trunk
Context
2018-05-04
00:39
Make a separate limb in the EXPLAIN QUERY PLAN output for the various lines associated with the OR-optimization. check-in: 75ac7b4e user: drh tags: trunk
2018-05-03
23:20
In ORDER BY LIMIT queries, try to evaluate the ORDER BY terms first, and it it becomes clear that the row will not come in under the LIMIT, then skip evaluation of the other columns. check-in: c381f0ea user: drh tags: trunk
22:52
Fix a branch that has become unreachable due to recent enhancements. check-in: 81ab5e0d user: drh tags: trunk
2018-04-30
19:32
Defer loading result column values into registers on an ORDER BY LIMIT until we know that the LIMIT does not exclude the current row. Closed-Leaf check-in: ce4ef460 user: drh tags: faster-order-by-limit
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Changes to src/select.c.

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  u8 nDefer;            /* Number of valid entries in aDefer[] */
  struct DeferredCsr {
    Table *pTab;        /* Table definition */
    int iCsr;           /* Cursor number for table */
    int nKey;           /* Number of PK columns for table pTab (>=1) */
  } aDefer[4];
#endif

};
#define SORTFLAG_UseSorter  0x01   /* Use SorterOpen instead of OpenEphemeral */

/*
** Delete all the content of a Select structure.  Deallocate the structure
** itself only if bFree is true.
*/
................................................................................
/* Forward reference */
static KeyInfo *keyInfoFromExprList(
  Parse *pParse,       /* Parsing context */
  ExprList *pList,     /* Form the KeyInfo object from this ExprList */
  int iStart,          /* Begin with this column of pList */
  int nExtra           /* Add this many extra columns to the end */
);

























































/*
** Generate code that will push the record in registers regData
** through regData+nData-1 onto the sorter.
*/
static void pushOntoSorter(
  Parse *pParse,         /* Parser context */
  SortCtx *pSort,        /* Information about the ORDER BY clause */
  Select *pSelect,       /* The whole SELECT statement */
  int regData,           /* First register holding data to be sorted */
  int regOrigData,       /* First register holding data before packing */
  int nData,             /* Number of elements in the data array */
  int nPrefixReg         /* No. of reg prior to regData available for use */
){
  Vdbe *v = pParse->pVdbe;                         /* Stmt under construction */
  int bSeq = ((pSort->sortFlags & SORTFLAG_UseSorter)==0);
  int nExpr = pSort->pOrderBy->nExpr;              /* No. of ORDER BY terms */
  int nBase = nExpr + bSeq + nData;                /* Fields in sorter record */
  int regBase;                                     /* Regs for sorter record */
  int regRecord = ++pParse->nMem;                  /* Assembled sorter record */
  int nOBSat = pSort->nOBSat;                      /* ORDER BY terms to skip */
  int op;                            /* Opcode to add sorter record to sorter */
  int iLimit;                        /* LIMIT counter */


  assert( bSeq==0 || bSeq==1 );













  assert( nData==1 || regData==regOrigData || regOrigData==0 );

  if( nPrefixReg ){
    assert( nPrefixReg==nExpr+bSeq );
    regBase = regData - nExpr - bSeq;
  }else{
    regBase = pParse->nMem + 1;
    pParse->nMem += nBase;
  }
  assert( pSelect->iOffset==0 || pSelect->iLimit!=0 );
  iLimit = pSelect->iOffset ? pSelect->iOffset+1 : pSelect->iLimit;
  pSort->labelDone = sqlite3VdbeMakeLabel(v);
................................................................................
    int regPrevKey;   /* The first nOBSat columns of the previous row */
    int addrFirst;    /* Address of the OP_IfNot opcode */
    int addrJmp;      /* Address of the OP_Jump opcode */
    VdbeOp *pOp;      /* Opcode that opens the sorter */
    int nKey;         /* Number of sorting key columns, including OP_Sequence */
    KeyInfo *pKI;     /* Original KeyInfo on the sorter table */

    sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase+nOBSat, nBase-nOBSat,regRecord);
    regPrevKey = pParse->nMem+1;
    pParse->nMem += pSort->nOBSat;
    nKey = nExpr - pSort->nOBSat + bSeq;
    if( bSeq ){
      addrFirst = sqlite3VdbeAddOp1(v, OP_IfNot, regBase+nExpr); 
    }else{
      addrFirst = sqlite3VdbeAddOp1(v, OP_SequenceTest, pSort->iECursor);
................................................................................
    ** If the new record does not need to be inserted into the sorter,
    ** jump to the next iteration of the loop. Or, if the
    ** pSort->bOrderedInnerLoop flag is set to indicate that the inner
    ** loop delivers items in sorted order, jump to the next iteration
    ** of the outer loop.
    */
    int iCsr = pSort->iECursor;
    int iJmp = sqlite3VdbeCurrentAddr(v)+5+(nOBSat<=0)+pSort->bOrderedInnerLoop;
    assert( pSort->bOrderedInnerLoop==0 || pSort->bOrderedInnerLoop==1 );
    sqlite3VdbeAddOp2(v, OP_IfNotZero, iLimit, sqlite3VdbeCurrentAddr(v)+4);
    VdbeCoverage(v);
    sqlite3VdbeAddOp2(v, OP_Last, iCsr, 0);
    sqlite3VdbeAddOp4Int(v, OP_IdxLE, iCsr, iJmp, regBase+nOBSat, nExpr-nOBSat);

    VdbeCoverage(v);
    sqlite3VdbeAddOp1(v, OP_Delete, iCsr);
  }
  if( nOBSat<=0 ){
    sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase+nOBSat, nBase-nOBSat,regRecord);
  }
  if( pSort->sortFlags & SORTFLAG_UseSorter ){
    op = OP_SorterInsert;
  }else{
    op = OP_IdxInsert;
  }
  sqlite3VdbeAddOp4Int(v, op, pSort->iECursor, regRecord,
                       regBase+nOBSat, nBase-nOBSat);





}

/*
** Add code to implement the OFFSET
*/
static void codeOffset(
  Vdbe *v,          /* Generate code into this VM */
................................................................................
  for(i=0; i<pEList->nExpr; i++){
    struct ExprList_item *pItem = &pEList->a[i];
    if( pItem->u.x.iOrderByCol==0 ){
      Expr *pExpr = pItem->pExpr;
      Table *pTab = pExpr->pTab;
      if( pExpr->op==TK_COLUMN && pTab && !IsVirtual(pTab)
       && (pTab->aCol[pExpr->iColumn].colFlags & COLFLAG_SORTERREF)
#if 0
          && pTab->pSchema && pTab->pSelect==0 && !IsVirtual(pTab)
#endif
      ){
        int j;
        for(j=0; j<nDefer; j++){
          if( pSort->aDefer[j].iCsr==pExpr->iTable ) break;
        }
        if( j==nDefer ){
          if( nDefer==ArraySize(pSort->aDefer) ){
................................................................................
  Vdbe *v = pParse->pVdbe;
  int i;
  int hasDistinct;            /* True if the DISTINCT keyword is present */
  int eDest = pDest->eDest;   /* How to dispose of results */
  int iParm = pDest->iSDParm; /* First argument to disposal method */
  int nResultCol;             /* Number of result columns */
  int nPrefixReg = 0;         /* Number of extra registers before regResult */


  /* Usually, regResult is the first cell in an array of memory cells
  ** containing the current result row. In this case regOrig is set to the
  ** same value. However, if the results are being sent to the sorter, the
  ** values for any expressions that are also part of the sort-key are omitted
  ** from this array. In this case regOrig is set to zero.  */
  int regResult;              /* Start of memory holding current results */
................................................................................
  }else if( eDest!=SRT_Exists ){
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
    ExprList *pExtra = 0;
#endif
    /* If the destination is an EXISTS(...) expression, the actual
    ** values returned by the SELECT are not required.
    */
    u8 ecelFlags;

    if( eDest==SRT_Mem || eDest==SRT_Output || eDest==SRT_Coroutine ){
      ecelFlags = SQLITE_ECEL_DUP;
    }else{
      ecelFlags = 0;
    }
    if( pSort && hasDistinct==0 && eDest!=SRT_EphemTab && eDest!=SRT_Table ){
      /* For each expression in p->pEList that is a copy of an expression in
      ** the ORDER BY clause (pSort->pOrderBy), set the associated 
      ** iOrderByCol value to one more than the index of the ORDER BY 
      ** expression within the sort-key that pushOntoSorter() will generate.
      ** This allows the p->pEList field to be omitted from the sorted record,
      ** saving space and CPU cycles.  */
      ecelFlags |= (SQLITE_ECEL_OMITREF|SQLITE_ECEL_REF);

      for(i=pSort->nOBSat; i<pSort->pOrderBy->nExpr; i++){
        int j;
        if( (j = pSort->pOrderBy->a[i].u.x.iOrderByCol)>0 ){
          p->pEList->a[j-1].u.x.iOrderByCol = i+1-pSort->nOBSat;
        }
      }
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
................................................................................
        ** composite primary keys in the SortCtx.aDefer[] array.  */
        VdbeOp *pOp = sqlite3VdbeGetOp(v, pSort->addrSortIndex);
        pOp->p2 += (pExtra->nExpr - pSort->nDefer);
        pOp->p4.pKeyInfo->nAllField += (pExtra->nExpr - pSort->nDefer);
        pParse->nMem += pExtra->nExpr;
      }
#endif











      regOrig = 0;








      assert( eDest==SRT_Set || eDest==SRT_Mem 
           || eDest==SRT_Coroutine || eDest==SRT_Output );
    }
    nResultCol = sqlite3ExprCodeExprList(pParse,p->pEList,regResult,

                                         0,ecelFlags);
#ifdef SQLITE_ENABLE_SORTER_REFERENCES


    if( pExtra ){
      nResultCol += sqlite3ExprCodeExprList(
          pParse, pExtra, regResult + nResultCol, 0, 0




      );
      sqlite3ExprListDelete(pParse->db, pExtra);





    }
#endif
  }

  /* If the DISTINCT keyword was present on the SELECT statement
  ** and this row has been seen before, then do not make this row
  ** part of the result.
  */
  if( hasDistinct ){
................................................................................
        sqlite3VdbeAddOp4Int(v, OP_Found, iParm+1, addr, r1, 0);
        VdbeCoverage(v);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm+1, r1,regResult,nResultCol);
        assert( pSort==0 );
      }
#endif
      if( pSort ){

        pushOntoSorter(pParse, pSort, p, r1+nPrefixReg,regResult,1,nPrefixReg);
      }else{
        int r2 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, r2);
        sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, r2);
        sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
        sqlite3ReleaseTempReg(pParse, r2);
      }







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  u8 nDefer;            /* Number of valid entries in aDefer[] */
  struct DeferredCsr {
    Table *pTab;        /* Table definition */
    int iCsr;           /* Cursor number for table */
    int nKey;           /* Number of PK columns for table pTab (>=1) */
  } aDefer[4];
#endif
  struct RowLoadInfo *pDeferredRowLoad;  /* Deferred row loading info or NULL */
};
#define SORTFLAG_UseSorter  0x01   /* Use SorterOpen instead of OpenEphemeral */

/*
** Delete all the content of a Select structure.  Deallocate the structure
** itself only if bFree is true.
*/
................................................................................
/* Forward reference */
static KeyInfo *keyInfoFromExprList(
  Parse *pParse,       /* Parsing context */
  ExprList *pList,     /* Form the KeyInfo object from this ExprList */
  int iStart,          /* Begin with this column of pList */
  int nExtra           /* Add this many extra columns to the end */
);

/*
** An instance of this object holds information (beyond pParse and pSelect)
** needed to load the next result row that is to be added to the sorter.
*/
typedef struct RowLoadInfo RowLoadInfo;
struct RowLoadInfo {
  int regResult;               /* Store results in array of registers here */
  u8 ecelFlags;                /* Flag argument to ExprCodeExprList() */
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
  ExprList *pExtra;            /* Extra columns needed by sorter refs */
  int regExtraResult;          /* Where to load the extra columns */
#endif
};

/*
** This routine does the work of loading query data into an array of
** registers so that it can be added to the sorter.
*/
static void innerLoopLoadRow(
  Parse *pParse,             /* Statement under construction */
  Select *pSelect,           /* The query being coded */
  RowLoadInfo *pInfo         /* Info needed to complete the row load */
){
  sqlite3ExprCodeExprList(pParse, pSelect->pEList, pInfo->regResult,
                          0, pInfo->ecelFlags);
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
  if( pInfo->pExtra ){
    sqlite3ExprCodeExprList(pParse, pInfo->pExtra, pInfo->regExtraResult, 0, 0);
    sqlite3ExprListDelete(pParse->db, pInfo->pExtra);
  }
#endif
}

/*
** Code the OP_MakeRecord instruction that generates the entry to be
** added into the sorter.
**
** Return the register in which the result is stored.
*/
static int makeSorterRecord(
  Parse *pParse,
  SortCtx *pSort,
  Select *pSelect,
  int regBase,
  int nBase
){
  int nOBSat = pSort->nOBSat;
  Vdbe *v = pParse->pVdbe;
  int regOut = ++pParse->nMem;
  if( pSort->pDeferredRowLoad ){
    innerLoopLoadRow(pParse, pSelect, pSort->pDeferredRowLoad);
  }
  sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase+nOBSat, nBase-nOBSat, regOut);
  return regOut;
}

/*
** Generate code that will push the record in registers regData
** through regData+nData-1 onto the sorter.
*/
static void pushOntoSorter(
  Parse *pParse,         /* Parser context */
  SortCtx *pSort,        /* Information about the ORDER BY clause */
  Select *pSelect,       /* The whole SELECT statement */
  int regData,           /* First register holding data to be sorted */
  int regOrigData,       /* First register holding data before packing */
  int nData,             /* Number of elements in the regData data array */
  int nPrefixReg         /* No. of reg prior to regData available for use */
){
  Vdbe *v = pParse->pVdbe;                         /* Stmt under construction */
  int bSeq = ((pSort->sortFlags & SORTFLAG_UseSorter)==0);
  int nExpr = pSort->pOrderBy->nExpr;              /* No. of ORDER BY terms */
  int nBase = nExpr + bSeq + nData;                /* Fields in sorter record */
  int regBase;                                     /* Regs for sorter record */
  int regRecord = 0;                               /* Assembled sorter record */
  int nOBSat = pSort->nOBSat;                      /* ORDER BY terms to skip */
  int op;                            /* Opcode to add sorter record to sorter */
  int iLimit;                        /* LIMIT counter */
  int iSkip = 0;                     /* End of the sorter insert loop */

  assert( bSeq==0 || bSeq==1 );

  /* Three cases:
  **   (1) The data to be sorted has already been packed into a Record
  **       by a prior OP_MakeRecord.  In this case nData==1 and regData
  **       will be completely unrelated to regOrigData.
  **   (2) All output columns are included in the sort record.  In that
  **       case regData==regOrigData.
  **   (3) Some output columns are omitted from the sort record due to
  **       the SQLITE_ENABLE_SORTER_REFERENCE optimization, or due to the
  **       SQLITE_ECEL_OMITREF optimization.  In that case, regOrigData==0
  **       to prevent this routine from trying to copy values that might
  **       not exist.
  */
  assert( nData==1 || regData==regOrigData || regOrigData==0 );

  if( nPrefixReg ){
    assert( nPrefixReg==nExpr+bSeq );
    regBase = regData - nPrefixReg;
  }else{
    regBase = pParse->nMem + 1;
    pParse->nMem += nBase;
  }
  assert( pSelect->iOffset==0 || pSelect->iLimit!=0 );
  iLimit = pSelect->iOffset ? pSelect->iOffset+1 : pSelect->iLimit;
  pSort->labelDone = sqlite3VdbeMakeLabel(v);
................................................................................
    int regPrevKey;   /* The first nOBSat columns of the previous row */
    int addrFirst;    /* Address of the OP_IfNot opcode */
    int addrJmp;      /* Address of the OP_Jump opcode */
    VdbeOp *pOp;      /* Opcode that opens the sorter */
    int nKey;         /* Number of sorting key columns, including OP_Sequence */
    KeyInfo *pKI;     /* Original KeyInfo on the sorter table */

    regRecord = makeSorterRecord(pParse, pSort, pSelect, regBase, nBase);
    regPrevKey = pParse->nMem+1;
    pParse->nMem += pSort->nOBSat;
    nKey = nExpr - pSort->nOBSat + bSeq;
    if( bSeq ){
      addrFirst = sqlite3VdbeAddOp1(v, OP_IfNot, regBase+nExpr); 
    }else{
      addrFirst = sqlite3VdbeAddOp1(v, OP_SequenceTest, pSort->iECursor);
................................................................................
    ** If the new record does not need to be inserted into the sorter,
    ** jump to the next iteration of the loop. Or, if the
    ** pSort->bOrderedInnerLoop flag is set to indicate that the inner
    ** loop delivers items in sorted order, jump to the next iteration
    ** of the outer loop.
    */
    int iCsr = pSort->iECursor;


    sqlite3VdbeAddOp2(v, OP_IfNotZero, iLimit, sqlite3VdbeCurrentAddr(v)+4);
    VdbeCoverage(v);
    sqlite3VdbeAddOp2(v, OP_Last, iCsr, 0);
    iSkip = sqlite3VdbeAddOp4Int(v, OP_IdxLE,
                                 iCsr, 0, regBase+nOBSat, nExpr-nOBSat);
    VdbeCoverage(v);
    sqlite3VdbeAddOp1(v, OP_Delete, iCsr);
  }
  if( regRecord==0 ){
    regRecord = makeSorterRecord(pParse, pSort, pSelect, regBase, nBase);
  }
  if( pSort->sortFlags & SORTFLAG_UseSorter ){
    op = OP_SorterInsert;
  }else{
    op = OP_IdxInsert;
  }
  sqlite3VdbeAddOp4Int(v, op, pSort->iECursor, regRecord,
                       regBase+nOBSat, nBase-nOBSat);
  if( iSkip ){
    assert( pSort->bOrderedInnerLoop==0 || pSort->bOrderedInnerLoop==1 );
    sqlite3VdbeChangeP2(v, iSkip,
         sqlite3VdbeCurrentAddr(v) + pSort->bOrderedInnerLoop);
  }
}

/*
** Add code to implement the OFFSET
*/
static void codeOffset(
  Vdbe *v,          /* Generate code into this VM */
................................................................................
  for(i=0; i<pEList->nExpr; i++){
    struct ExprList_item *pItem = &pEList->a[i];
    if( pItem->u.x.iOrderByCol==0 ){
      Expr *pExpr = pItem->pExpr;
      Table *pTab = pExpr->pTab;
      if( pExpr->op==TK_COLUMN && pTab && !IsVirtual(pTab)
       && (pTab->aCol[pExpr->iColumn].colFlags & COLFLAG_SORTERREF)



      ){
        int j;
        for(j=0; j<nDefer; j++){
          if( pSort->aDefer[j].iCsr==pExpr->iTable ) break;
        }
        if( j==nDefer ){
          if( nDefer==ArraySize(pSort->aDefer) ){
................................................................................
  Vdbe *v = pParse->pVdbe;
  int i;
  int hasDistinct;            /* True if the DISTINCT keyword is present */
  int eDest = pDest->eDest;   /* How to dispose of results */
  int iParm = pDest->iSDParm; /* First argument to disposal method */
  int nResultCol;             /* Number of result columns */
  int nPrefixReg = 0;         /* Number of extra registers before regResult */
  RowLoadInfo sRowLoadInfo;   /* Info for deferred row loading */

  /* Usually, regResult is the first cell in an array of memory cells
  ** containing the current result row. In this case regOrig is set to the
  ** same value. However, if the results are being sent to the sorter, the
  ** values for any expressions that are also part of the sort-key are omitted
  ** from this array. In this case regOrig is set to zero.  */
  int regResult;              /* Start of memory holding current results */
................................................................................
  }else if( eDest!=SRT_Exists ){
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
    ExprList *pExtra = 0;
#endif
    /* If the destination is an EXISTS(...) expression, the actual
    ** values returned by the SELECT are not required.
    */
    u8 ecelFlags;    /* "ecel" is an abbreviation of "ExprCodeExprList" */
    ExprList *pEList;
    if( eDest==SRT_Mem || eDest==SRT_Output || eDest==SRT_Coroutine ){
      ecelFlags = SQLITE_ECEL_DUP;
    }else{
      ecelFlags = 0;
    }
    if( pSort && hasDistinct==0 && eDest!=SRT_EphemTab && eDest!=SRT_Table ){
      /* For each expression in p->pEList that is a copy of an expression in
      ** the ORDER BY clause (pSort->pOrderBy), set the associated 
      ** iOrderByCol value to one more than the index of the ORDER BY 
      ** expression within the sort-key that pushOntoSorter() will generate.
      ** This allows the p->pEList field to be omitted from the sorted record,
      ** saving space and CPU cycles.  */
      ecelFlags |= (SQLITE_ECEL_OMITREF|SQLITE_ECEL_REF);

      for(i=pSort->nOBSat; i<pSort->pOrderBy->nExpr; i++){
        int j;
        if( (j = pSort->pOrderBy->a[i].u.x.iOrderByCol)>0 ){
          p->pEList->a[j-1].u.x.iOrderByCol = i+1-pSort->nOBSat;
        }
      }
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
................................................................................
        ** composite primary keys in the SortCtx.aDefer[] array.  */
        VdbeOp *pOp = sqlite3VdbeGetOp(v, pSort->addrSortIndex);
        pOp->p2 += (pExtra->nExpr - pSort->nDefer);
        pOp->p4.pKeyInfo->nAllField += (pExtra->nExpr - pSort->nDefer);
        pParse->nMem += pExtra->nExpr;
      }
#endif

      /* Adjust nResultCol to account for columns that are omitted
      ** from the sorter by the optimizations in this branch */
      pEList = p->pEList;
      for(i=0; i<pEList->nExpr; i++){
        if( pEList->a[i].u.x.iOrderByCol>0
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
         || pEList->a[i].bSorterRef
#endif
        ){
          nResultCol--;
          regOrig = 0;
        }
      }

      testcase( regOrig );
      testcase( eDest==SRT_Set );
      testcase( eDest==SRT_Mem );
      testcase( eDest==SRT_Coroutine );
      testcase( eDest==SRT_Output );
      assert( eDest==SRT_Set || eDest==SRT_Mem 
           || eDest==SRT_Coroutine || eDest==SRT_Output );
    }

    sRowLoadInfo.regResult = regResult;
    sRowLoadInfo.ecelFlags = ecelFlags;
#ifdef SQLITE_ENABLE_SORTER_REFERENCES
    sRowLoadInfo.pExtra = pExtra;
    sRowLoadInfo.regExtraResult = regResult + nResultCol;
    if( pExtra ) nResultCol += pExtra->nExpr;


#endif
    if( p->iLimit
     && (ecelFlags & SQLITE_ECEL_OMITREF)!=0 
     && nPrefixReg>0
    ){

      assert( pSort!=0 );
      assert( hasDistinct==0 );
      pSort->pDeferredRowLoad = &sRowLoadInfo;
    }else{
      innerLoopLoadRow(pParse, p, &sRowLoadInfo);
    }

  }

  /* If the DISTINCT keyword was present on the SELECT statement
  ** and this row has been seen before, then do not make this row
  ** part of the result.
  */
  if( hasDistinct ){
................................................................................
        sqlite3VdbeAddOp4Int(v, OP_Found, iParm+1, addr, r1, 0);
        VdbeCoverage(v);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm+1, r1,regResult,nResultCol);
        assert( pSort==0 );
      }
#endif
      if( pSort ){
        assert( regResult==regOrig );
        pushOntoSorter(pParse, pSort, p, r1+nPrefixReg, regOrig, 1, nPrefixReg);
      }else{
        int r2 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, r2);
        sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, r2);
        sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
        sqlite3ReleaseTempReg(pParse, r2);
      }

Changes to src/sqliteInt.h.

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  int iIdxCur;              /* Index of the first index cursor */
};

/*
** An instance of the following structure contains all information
** needed to generate code for a single SELECT statement.
**
** nLimit is set to -1 if there is no LIMIT clause.  nOffset is set to 0.
** If there is a LIMIT clause, the parser sets nLimit to the value of the
** limit and nOffset to the value of the offset (or 0 if there is not
** offset).  But later on, nLimit and nOffset become the memory locations
** in the VDBE that record the limit and offset counters.
**
** addrOpenEphm[] entries contain the address of OP_OpenEphemeral opcodes.
** These addresses must be stored so that we can go back and fill in
** the P4_KEYINFO and P2 parameters later.  Neither the KeyInfo nor
** the number of columns in P2 can be computed at the same time
** as the OP_OpenEphm instruction is coded because not
** enough information about the compound query is known at that point.







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<
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<







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  int iIdxCur;              /* Index of the first index cursor */
};

/*
** An instance of the following structure contains all information
** needed to generate code for a single SELECT statement.
**
** See the header comment on the computeLimitRegisters() routine for a
** detailed description of the meaning of the iLimit and iOffset fields.



**
** addrOpenEphm[] entries contain the address of OP_OpenEphemeral opcodes.
** These addresses must be stored so that we can go back and fill in
** the P4_KEYINFO and P2 parameters later.  Neither the KeyInfo nor
** the number of columns in P2 can be computed at the same time
** as the OP_OpenEphm instruction is coded because not
** enough information about the compound query is known at that point.